A facile synthesis based on the addition of ascorbic acid to a mixture of Na2PdCl4, K2PtCl6 and Pluronic P123 results in highly branched core-shell nanoparticles (NPs) with unique micro-mesoporous dandelion-like morphology comprising Pd core and Pt shell. The slow reduction kinetics associated with the use of ascorbic acid as a weak reductant and suitable Pd/Pt atomic ratio (1/1) play a principal role in the formation mechanism of such branched Pd@Pt core-shell NPs, which differs from the traditional seed mediated growth. The catalyst efficiently achieves the reduction of a variety of olefins in good to excellent yields. Importantly, higher catalytic efficiency of dandelion-like Pd@Pt core-shell NPs was observed for the olefin reduction when compared to commercially available Pt black, Pd NPs and physically admixed Pt black and Pd NPs. This synergistic effect and superior catalytic behavior is not only due to larger surface area but also due to unique micro-mesoporous structure with significant contribution of mesopores with sizes of several tens of nanometers.